This invention relates to vehicle suspensions, and more particularly to control valves used in controlled damper vehicle suspension systems.
Vehicle suspension systems utilize dampers, such as MacPherson struts or shock absorbers, to improve stability and handling of the vehicle by damping the speed at which the vehicle wheels can move vertically with relation to the vehicle body as the wheels encounter road obstacles, or the body sways in response to steering or other maneuvers incident with driving the vehicle. To optimize performance of the vehicle during both normal slow speed maneuvering of the vehicle, and during high speed maneuvering, some vehicle suspension systems actively control performance of the dampers with a control system having control valves that modulate a flow of hydraulic fluid to the dampers. By increasing or decreasing the pressure and/or rate of fluid flow through the control valve to and from the dampers, the control system can modify the stiffness of the dampers to optimize damper performance as a function of vehicle operation.
A typical valve of the type used for controlling dampers includes generally cup-shaped valve spool 100 having an annular cylindrical wall 102 extending from a closed end 104 along a spool axis 106, as depicted in FIGS. 1a-1c. The annular wall 102 includes side flow openings, in the form of slots 103. The outer surface of the annular wall on either side of the slots 103 defines land areas 108, 110 having a diameter that produce a close tolerance sliding fit of the spool 100 within a bore (not shown) of the valve.
The bore and spool 100 are configured such that the spool 100 can be moved linearly in the bore along the spool axis 106. The sidewall of the bore includes radially directed fluid ports that allow fluid to pass in to or out of the bore. When the spool 100 is positioned in the bore with one of the lands 108, 110 blocking the fluid ports in the sidewall of the bore, fluid cannot flow in or out of the ports. When the spool 100 is positioned in the bore with the slots 103 at least partially overlapping the ports in the sidewall of the bore, fluid can flow through the fluid path formed by the slots 103 and the portion of the ports overlapping the slots 103. Full flow is achieved when the fluid ports are totally uncovered by the slots 103.
The spool 100 is positioned linearly by an actuator mechanism (not shown). The valve may include a spring acting against the open end 112 of the spool and having a pre-load for moving the spool linearly to the left, as depicted in FIGS. 1a-1c, in the bore to move one or both of the lands 108, 110 over the ports in the bore sidewall to block flow through the valve. The actuator may include a movable element bearing against the closed end 104 of the spool 100 for pushing the spool 100 linearly in the bore against the force of the spring, to align the slots 103 and lands 108, 110 partially or filly over the fluid ports in the sidewall of the bore, to thereby regulate fluid flow through the valve. The closed end 104 of the spool may include equalizing orifices 114 to provide a path for fluid in the bore to pass through the closed end 104 of the spool 100, so that the spool 100 can move freely in the bore.
While valves having a spool 100 configured as described above may work well in many applications, this type of valve has exhibited a degree of flow-induced instability that is unacceptable for use in controlling vehicle dampers.
What is needed, therefore, is an improved valve for regulating fluid flow in a controlled damper vehicle suspension, that provides a solution to one or more of the problems described above.
Our invention provides improved resistance to flow induced instability in a control valve for a vehicle damper, through the use of a generally tubular shaped valve spool having an open, bridged, flow-through end, rather than side flow openings. The flow-through end of the spool has a narrow flat edge oriented perpendicularly to the axis of the spool, with an inside surface of the spool forming a 55 to 90 degree angle with the flat edge, and meeting the flat edge in a sharp corner. In addition to the improved performance achieved in a valve according to our invention, elimination of the side flow openings and closed end of prior spool configurations allows the valve spool in our valve to be shorter than the spools used in prior control valves for vehicle dampers, thereby allowing a control valve according to our invention to be smaller in size and lighter in weight than prior control valves.
In one form of our invention, a valve spool, adapted for linear movement in a bore and for regulating fluid flow through fluid ports entering the bore through a sidewall of the bore, includes a generally tubular cylindrical body having an annular wall defining an axis of the spool, a wall thickness of the spool, and inner and outer cylindrical surfaces of the spool extending between a first and a second axial end of the spool. The outer cylindrical surface of the spool defines a cylindrical land at the second axial end of the spool adapted to slidingly mate with the sidewall of the bore, and having an axial land length sufficient to block flow through the fluid ports of the bore when the spool is positioned within the bore with the land covering the fluid ports. The first end of the spool is adapted for receipt of spring means for urging the spool to move in a first linear direction within the bore, to position the land to block the fluid ports. The second end of the spool is generally open for the passage of fluid, and includes a bar extending laterally across the second end of the spool. The bar is adapted to receive a pin from an actuator extending through the bore, for moving the spool linearly in the bore in a second direction, to compress the spring means and move the second end of the spool to a position within the bore where the ports are at least partially open beyond the second end of the spool. The spool wall and bar at the second end of the spool define substantially sharp corners. The resulting spool configuration reduces linear movement of the spool in the bore when fluid is flowing through the spool, thereby resulting in significantly enhanced stability of the valve.
Our invention may also take the form of a control valve including a valve spool of the form described above. The control valve may also include spring means and actuator means for controlling the position of the spool in the bore.
The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.